This research is comprised of two main parts. Firstly, burst pressures in vessel components are evaluated. Two types of failure mode are investigated, one due to excessive plastic deformation and the other due to plastic instability. Experimental tests, carried out on components made from mild steel, aluminium alloy 6061, and stainless steel 316/316L, provide good verification results. For burst pressure due to excessive plastic deformation, a numerical method for determination of its value in shallow spherical caps and torispheres subject to internal pressure is proposed. Burst pressure is defined as the maximum pressure at which a proposed plastic strain criterion is met. Plastic instability pressure is known as the maximum load at which a small load increment causes a very large deformation. For toroidal shells under internal pressure, a closed-form formula of plastic instability condition is derived. Then the corresponding pressure at instability is obtained by semi-analytical analysis. This pressure is also predicted by finite element analysis. Secondly, modern optimisation techniques including Simulated Annealing, Particle Swarm Optimization and Differential Evolution have been applied to the design of minimum weight toroidal vessels subject to internal pressure. Constraints are the first yield' pressure, plastic pressure, burst pressure and volume contained by the toroid. Optimality includes geometry and wall thickness. Shells are made from mild steel with constant or variable wall thickness. The optimisation process is performed by a rou!ine written in FORTRAN coupled with finite element analysis code ABAQUS. Depending on geometry parameters of the toroid, the material saving can be as high as 72%. The results show that Differential Evolution is the best method.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:502223 |
| Date | January 2008 |
| Creators | Vu, Vu Truong |
| Publisher | University of Liverpool |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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